Method of and apparatus for concentrating nitric acid



Jan. 3l, 1933. J, H SHAPLEIGH 1,895,492

METHOD OF AND APPARATUS FOR CONCENTRATING NITRIC ACID Filed Oct. 17.1929 F/GJ.

5y aan lf;

A raf/vin?.

Patented Jianyll, 1933 q UNITED `s'rxrlzs* PATENT; OFFICE i JAMES n.SHAPLETGH, or MOUNT LAKES, NEW JERSEY, ASSIGNOR To HERCULES POWDERCOMPANY, or WILMINGTON, DELAWARE, A CORPORATION or DELAWARE METHOD ANDAPPARATUS FORCONCENTRATING NITRIC .ACID

i Application filed October 17, 1929.` Serial No. 400,198.

This invention relates to a process of concentrating nitric acid andapparatus Vtherel for; `and'has more particular reference to a processinvolvingthe treatment ofthe dilute acid with a dehydrating agentfollowed by the vaporization of concentrated ,nitric acid from themixture. 'i

In concentrating nitric acid bythe treatment thereof with a dehydratingagent such as sulphuric acid, it was first proposed that thenitric acidcould be vaporizedffrom the Y mixture as it passed through a packedcolumn by the application ofexternal heat. Various disadvantages arosein carrying out this process'because of overheatingwhich resulted in theformation of nitrososulphuric acid and V On the.

decomposition Vof the nitric acid.

Y other hand, if a lowtemperature was used tolavoid overheating,thenitric acid Vwas not completelyv removed from the residual acid. fAttempts to improve this process by causing hol-gases to flowincouutercurrent relasod i A tionship with the acidic mixture hadsimilarobjectionable features and in addition resulted in a loss of acid in theexhausted gases.

A more satisfactory process resulted when steam was used in place ofthehot gases in-` asmuch as the steam was absorbed in the vacid f mixturewhereby its latent heat of vaporizan tion and heat ofcombination withsulphurio facid became vavailable to evaporate the nitric acid. In thisprocess, since the temperature never rose substantially above theboiling point of the mixture at any point, overheating `was avoided. Itwas found, however,

that the limit of economyin this process was reached when the residualacid had a strength f of 62465% HgSOi. Any attempt to decrease thesulphuric acid .component to give a more economical use of the sulphuricacid resulted in'an incompletelydenitrated product. This failure of theprocess is due to the fact that Vthe boiling `points v-of mixturespassing through the tower first rise and then fall,-V fmaking itimpossible to. use steam with mix- -ratio of nitric acid scendedandnitric acid' was vaporized, the

of concentrated nitric acid may -beobtained from a mixture containing42% HN03, 38%

H2SO4 land 20% H2O. On the other hand,

the most economical results from the process using steam as abovedescribed necessitate a mixture rich in sulphuric acid, as representedby the composition 27 .5% HNOS,

HZSO. H20. v K

`The objects of the improved process involving the attainmenty of higheconomy of sulphuric acid will be apparent from the followingdescription of a desirable form of apparatus and,` its use read inconjunction with the accompanying drawing in which:

Fig. l is an elevation, partly in section, of a` concentra-ting tower;and

Fig.2 is a perspective view of a heating element used in the tower. y y

The apparatus consists of a tower 2 of the ,usual construction used inconcentration or `and gases passing therethrough. Steam or `some otherhot gaseous medium enters the bottom of the tower at 6, an exit 8 beingprovided at the bottomof the tower for the residual mixture of sulphuricacid and water.

The mixture of acids is led into the top ofthe tower through a pipe 10,the lower end of which terminates in a spray head l2 arranged to spreadthe acids over the packing. An exit pipe 14 leads the concentratednitric acidvapors to al suitable condenser.

In the lower portions of the tower are located perforated heater plates16 adapted to be heated by steam or other hot gases passing throughcoils 18 therein or by electricity through resistance coils therein. Thepacking 4 fills the spacesbetween these plates as well as the upperportions of the tower.

In the method heretofore used involving `the passage of .steam incountercurrent relationship to the downwardly flowing acid mixture, itwas necessary to start with a mixture containing a sufliciently largepercentage of snlphuric acid so that, as the mixture deboiling point ofthe remaining acid mixture would continue to rise until the bottom ofthe tower was reached. This'necessitated a recontaining at least fiedwas found to contain 58% H280..

' f' 11,80* nitric acid obtained was of 95% strength. vis ll'uodwhavignlower oon- This grocess represents thouseA oi 90 par@ HSG Y'msidnd'amidwould of H, 0 per 100 parts ofi-IND. ascompmgf* n '.5 the boiling pointswould with the use of 230 arts of HzO.

. i; J' a nv .33: NHNOg in l'fmlenp.4

fwold not carried dt without th use of lmfded' extent aftez'rgothe'awhile there hsteen'describedsone n paratus an e, as nppln jwifibenwmn"4 tlmv eni'atin Offone I :f-It'w'll' bo ulicerstood thatl:Egel"giidtzions'of*the q r f inou-processwillvary .whghf'inixws `emut1n an ap o the kind'dep1oyedl since .any mixture having concen llldingan' uprightxwwelgg V Yfis y rectly heating within the tower, a conduitfor leading a mixture of nitric acid, sulphuric acid and water into thetop of the tower, a conduit for leading nitric acid vapors from the topof the tower, a conduit for leading-a hot gaseous medium into thebottomof the tower, a conduit for leading liquid from the bottom of the tower,and heating meansv adapted to impart heat to the mixture therein, saidheating means comprising perforated plates arranged 'transversely to thetower and means for heating the plates.

3. The method of concentrating nitric acid, including flowing a mixtureof nitric acid,

sulphuric acid and water through a path, di-

the mixture internally v throughout its flow in the path and in aportion ofthe path subjecting the mixture additionally to indirectexternal heating.

4. .The method of concentrating nitric acid including flowinga mixtureof nitric acid, sulphuric acid and Water through a path,

f counterflowing steam with the mixture Y to;

f through the path and in a portion of the path subjecting the mixturein its flow to indirect heating.l Y Y 5. An'apparatus for concentratingnitric acid including means forming an enclosed passage, vmeans forintroducing nitric acid,

sulphuric acid and water into the passage,

a conduit for leading nitric acid vapors from the passage, a conduit forleading hot gaseous medium from an external source into the passage, aconduit for leading liquid from the passage and indirect heating meansadapted for heating the interior of the passage at a point spaced fromthe point of introduction of said acids and water and between the pointof introduction thereof and the point-of introduction of said hotgaseous medium.

6. An apparatus for concentrating nitric i acid including means formingan enclosed passage, means for introducing nitric acid, sulphuric acidand water into the passage, a conduit for leading nitric acid vaporsfrom the passage, a conduit for leading hot gasepassage.

7'. Thev method of concentrating nitricacid which includesVcounterllowing a mixture of nitric acid, sulphuric acid and water witha hot gaseous medium introduced from an external source into the path offlow of the `finixture whereby the mixture Vis directly heated in itsinitial fiow and simultaneously7 indirectly heating the mixture during apart of its counterow with the hot gaseous medium and while the mixturestill contains a substantial amount of nitric acid.

8. The method of concentrating nitric acid which includes counterliowinga. mixture of nitric acid, sulphuric acid and water with steamintroduced from an external source into the path of flow of the mixturewhereby the mixture is directly heated in its initial flow andsimultaneously indirectly heating the mixture during a part of itscountertlow with the steam and while the mixture still contains asubstantial amount of nitric acid. 9. The method of concentrating nitricacid which inciudes counterflowing a mixture of nitric acid, sulphuricacid and water, the nitric and sulphuric acids being in about theproportion of one to one, with a hot gaseous medium introduced from `anexternal source into the path of ow ofthe mixture whereby the mixture isdirectly heated in its initial dow and simultaneously indirectly heatingthe mixture during a part of its counteriiow with the steam and whilethe mixture still contains a substantial amount of nitric acid. Y ntestimony of which invention, I have hereunto set my hand, at Kenvil, N.J., on

JAMES H. SHAPLEIGH.

